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Fan Dipole Ladder Line

Jul 16th, 16:57

W3NSH

Joined: Jun 5th 2019, 11:23
Total Topics: 0
Total Posts: 0
This is my first antenna build and I want to do a fan dipole that covers at least 80, 40, 20 and maybe 17 and 10m. I have a 50 ft length of RG-8x with PL259s already soldered on. Can I first feed the dipole with homebrew open ladder line and then use a 4:1 balun to attach the coax and go into my shack? If I can get the antenna up 40-50 ft. I won't have enough coax to get to my radio, hence the ladder line. I also read that using ladder line allows me more bandwidth. I'd like to use the SSB and digital mode portions of the bands.How do I determine how far I should space the width of my ladder line for a homebrew version?
Jul 16th, 20:01

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
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Total Posts: 0
I haven't tried this so I don't know if this will really work.
If you use folded dipoles that will step up the impedance to match the step up of the 4:1 balun. Thus, you may be able to use 200 ohm open wire.
https://owenduffy.net/calc/tl/twllc.htm
Owen has a open wire calculator on his web site.
200 ohms requires a rather narrow spacing and thus more insulators that typical installations.

This is a pretty involved project for a first antenna. I'd suggest starting off with a simpler antenna, perhaps a single band dipole for 20 or 40 meters.

Zak Lau W1VT
ARRL Senior Lab Engineer

Jul 19th, 13:16

AA6E

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Zak is right that a single band dipole is lots easier than a true multiband fan system. (Apart from mechanical issues, all the dipoles interact with each other, making it hard to get good SWR on all bands.)

I have had good luck with a "non-resonant" dipole system, with 86 ft length fed by 400 ohm ladder line. The ladder line ("any length") comes into the house, where I have a 4:1 balun giving 50 ohm impedance, more or less. You do require an antenna tuner, however, to get reasonable SWR. It does cover 80 - 6 M pretty well for me. (Thanks WB1GCM for the tip.)

73 Martin AA6E

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